Atherosclerosis and atherosclerosis related complications such as heart attack, stroke, and angina, are the leading cause of death in the western world, and effective treatments are greatly needed. A key issue limiting the treatment of atherosclerosis is an inability to diagnose atherosclerotic plaques that have a high risk of growing and rupturing, also known as active plaques. The overproduction of reactive oxygen species (ROS) is necessary for the growth and rupture of atherosclerotic plaques, making ROS an excellent diagnostic marker for active plaques. The objective of this application is to develop a new family of fluorescent contrast agents, termed the hydrocyanines, which have the physical and chemical properties needed to image ROS in atherosclerotic plaques, in the carotid artery, and detect plaque activity. The hydrocyanines are a new family of fluorescent dyes, recently developed in our laboratory, which can detect ROS at nanomolar concentrations, have tunable emission wavelengths ranging from 570-810 nm, and accumulate within cells after oxidation. Our approach is to image ROS in the carotid artery of mice and rabbits, suffering from vascular injury and atherosclerosis, with the hydrocyanines. The central hypothesis of this proposal is that: The hydrocyanines have the physical and chemical properties needed to detect oxidative stress in the carotid artery and detect plaque activity. This hypothesis is based on our preliminary data, which demonstrates that the hydrocyanines can detect superoxide and the hydroxide radical in cell culture, in tissue samples and for the first time in vivo. The overall objective of this proposal will be accomplished by testing our central hypothesis through the following three Specific Aims; Specific Aim I: Optimize the hydrocyanines using the kinetic isotope effect Specific Aim II: Detect ROS production in a murine model of carotid artery injury Specific Aim III: Detect ROS production by atherosclerotic tissues in vivo in a rabbit model of atherosclerosis and ex-vivo in diseased human coronary arteries The experiments in this proposal will determine if the hydrocyanines can image ROS in atherosclerotic plaques and detect plaque activity in mice and rabbits. The experiments in this proposal are innovative because they will lead to the development of a contrast agent that can image ROS, in vivo, for the first time. This proposal is also significant because it will generate a new class of diagnostics, which have the potential to diagnose patients at risk of developing heart attacks and strokes. Furthermore, numerous other diseases are also associated with an overproduction of ROS, such as cancer and neurodegenerative disease; we therefore anticipate that the results of this proposal will impact several areas of medicine and biology.